Mercuric Halide Adducts of Polyethers
Inorganic Chemistry, Vol. 15, No. 8, 1976 1791 Contribution from the Department of Chemistry, Northland College, Ashland, Wisconsin 54806
Information on Structure and Basicity from the Nuclear Quadrupole and Infrared Spectra of Mercuric Halide Adducts of Polyethers and a Crown Ether l a GARY WULFSBERGlb AIC506349 The halogen NQR frequencies and Hg-C1 ir stretching frequencies of the mercuric halide adducts of the polyethers RO(CH2CH20),1R (R = CH3 or (CH3)3C, n = 2-5,7) and the crown ether (CH$H20)6 have been recorded and analyzed in terms of the number of oxygen donor atoms per mercury atom n and the number of intermolecular halogen-mercury interactions present in the adducts, as judged by molecular models and published crystal structures. It is found that each C1-Hg intermolecular interaction lowers the 35ClNQR frequency by 0.7-1.5 MHz; the factor n has a smaller effect of -0.6 MHz per donor atom. If these factors are first taken into account, the NQR frequencies or Hg-Cl stretching frequencies of HgX2 adducts of oxygen Lewis bases can then give information on the relative basicity of the oxygen base or reveal any unusual coordination environment of the mercury. Several examples of the latter are discussed, including mercuric bromide-triglyme, which shows a phase transition between monomer and dimer forms, and HgC12 itself, which should be used only with caution as a reference point in solid-state ir or NQR studies.
Received August 25, 1975
Hg were about 1% low. For HgBrygly, glyme was determined by Introduction weight loss on prolonged exposure to air. For HgC12.18-crown-6, it The chlorine, bromine, and iodine nuclear quadrupole was necessary to add detergent to the reaction mixture to obtain resonance (NQR) spectra of many derivatives of the mercury sufficient solubility of the sample for the Rupp method. HgBrz. halides have been studied, including the mercuric halides 18-crown-6gave very low analysis by the Rupp method even with themselves,2 the adducts of the mercuric halides with organic prolonged digestion with detergent, while HgI2.18-crown-6was so Lewis bases (usually having oxygen donor atom^),^-^ the insoluble that it gave no detectable mercury. However, excellent carbon-hydrogen analyses were obtained for these three adducts. All complex chloro anions of mercury,1° and various organoanalytical data are reported in Table 1 of the supplementary material. mercury halides.' Related..quadrupole coupling constants 35ClNQR spectra were measured at 77 K and at ambient temhave also been obtained by M o s ~ b a u e rand ' ~ microwave20-21 perature (ca. 304 K) on a Decca Radar NQR spectrometer with spectroscopy. But the interpretation of these NQR frequencies Zeeman modulation and are accurate to f0.005 MHz. 79Br,81Br, is complex due to the many factors which may affect the &/2) frequencies were recorded on a Wilks and 1271 ( f l / 2 halogen directly or modify the mercury-halogen covalent bond. NQR- 1A spectrometer at room temperature, which was measured An incomplete listing of the factors previously suggested would with a thermometer and held relatively constant by means of an air include (1) the inductive effect of the Q substituent in QHgCl, stream directed at the coil and sample. The sidebands present in these (2) the electron-donating effect of each donor atom in a Lewis spectra may conceal some slightly split doublet signals. Some halogen base adduct, (3) the number of donor atoms about mercury, NQR signals might also have been missed due to unfavorable relaxation times, which would of course alter the structural interpretation. (4) any weak coordinatecovalent or Sternheimer22 interaction Frequencies were calibrated using external reference samples of HgBrl of the halogen itself with mercury atom(s) in other molecules, and KBrO3; bromine frequencies were interpolated to f0.3 MHz, and (5) any partial mercury-halogen triple bonding. As an while most iodine frequencies were extrapolated to f0.7 MHz. apparent conse uence of this number of factors, the NQR Solid-state ir spectra (1400-250 cm-l) were obtained as Nujol mulls frequencies of C1 bonded to mercury occur over the wide on polyethylene sheets between CsI plates and were found to be very range of 8 to more than 23 MHz, and their detailed intersimilar to the results obtained by I ~ a r n o t o .Solution ~~ ir spectra pretation remains unclear. (429-250 cm-l) were obtained in benzene solution in 2-mm polyIn this paper we report a study of the 1:l adducts of HgCl2, ethylene cells on a Perkin-Elmer Model 457 ir spectrometer. HgBr2, and HgI2 with the following polyethers ROFramework molecular models were used to assess geometrical constraints. (CH2CH20),1R: glyme, gly ( R = CH3, n = 2 ) ; diglyme, digly ( R = CH3, n = 3); diglytbu (R = (CH3)3C, n = 3 ) ; Hypotheses and Theory triglyme, trigly ( R = CH3, n = 4); tetraglyme, tetragly ( R In this series of adducts many of the five factors mentioned = CH3, n = 5 ) ; and the cyclic (crown) ether 18-crown-6, in the Introduction can be controlled: (1) the substituent on (CH2CH20)6. (Only the combination glyme + HgI2 failed mercury is always C1, Br, or I; (2) all oxygen donor atoms to give an isolable adduct.) In addition we studied the 2:l should be of similar basicity; and (5) any mercury-halogen hexaglyme adducts ~ H ~ X T C H ~ O ( C H ~ C H ~ where O ) ~ C H ~triple-bonding , character (which is often not considered imX = C1, Br, and I. portant in any case) should be nearly constant for each halogen. Hence only two important variable factors remain. Experimental Section In the 1:l adducts factor 3, the number of donor atoms Mercuric halides were analytical reagent grade and were used about mercury (which we will symbolize by n), would equal without further purification. Polyethers, used without further puthe number of oxygen atoms in the polyether, if the polyether rification, were obtained from the Aldrich Chemical Co., except for adopts a completely chelating conformation. 1 w a m o t 0 ~has ~ diglytbu (diethylene glycol di-tert-butyl ether), from Dow Chemical Co., and hexaglyme (hexagly; 2,5,8,11,14,17,20-heptaoxaheneicosane), shown by x-ray crystallography that this is so for the adducts from Schuchardt, Munich. Adducts were prepared by either or both HgClTtetragly and HgClTtetraglyet ( R = CH3CH2, n = 5 ) , of two methods: (1) the mercuric halide was dissolved in an excess and he has analyzed the ir spectra of the polyether ligands in of hot polyether and cooled; (2) stoichiometricquantities of polyether the HgC12 and HgBrz adducts of glyme, diglyme, and triand mercuric halide were combined in hot ethanol, and the solution g l ~ m e to , ~ show ~ that their conformations are similar. was cooled. Mercury was determined iodometrically by the Rupp Iwamoto's x-ray dataZ4 on the above and more complex method, using gelatin as a protective colloid.23 For analysis, the polyether-mercuric chloride adducts show H g - 0 distances adducts of the higher ethers were rinsed three times with Skelly B of 2.66-2.96 A and 0-Hg-0 angles of 59-64', These are and then vacuum-dried to constant weight; satisfactory analyses were substantially the same as the K-0 distances and 0-K-0 obtained. For the diglyme adducts, the coordinated polyether was too readily lost, so that air-drying was used; consequently results for angles found25 in the especially stable crown ether adducts of
-
9
1792 Inorganic Chemistry, Vol. 15, No. 8, 1976
Gary Wulfsberg
Table I. Intermolecular Interactions Predicted in Polyether Adducts Using Molecular Models Compd
CN- CN- CN(HgY ( X I ) (X,)
State of aggregation
HgBrz, yellow HgI,b HgBr,.THFb HgCI,. 2CH,0Hb HgC1, ,dioxb
6
3 --3
Layer polymer
6 6
2 2
3 2
Layer polymer Linear polymer
6
2
2
HgX,.gly HgX,.digly HgX,.diglytbu
6 6 5 or 6 6or 7 6
2 1 1
1
2 2 1 or 2 lor 2 1
Linear polymer cross-linked by dioxane Puckered linear polymer Dimer Monomer or dimer
7 8
1
1
1
1
7
1
2
HgX, .trigly HgBr .2dioxb HgC1, ,tetraglyb HgX,. 18-crown-6 2HgC1,. hexaglyetb
1
Monomer or dimer Monomer cross-linked b y dioxane in two dimensions Monomer Monomer Monomer with two HgC1, units
CN(Hg) is t h e coordination number of mercury; CN(X,) and CN(X2) are the coordination numbers of halogen atoms 1 and 2. From t h e crystal structure (see t e x t for references).
18-crown-6 and K+. As we also observe the ir spectra of the crown ether ligand in the HgX2 and K+ adducts to be very similar, we take as our working hypothesis that, in general, in the above adducts each polyether oxygen atom is coordinated to mercury and that the ligand is completely chelating. Factor 4, the number of weak intermolecular halogenmercury interactions, was then assessed using molecular models with the H g - 0 distances and 0-Hg-0 angles just cited,24 conventional26Hg and halogen covalent radii, van der Waals radii, etc. (There is dispute as to the value of the Hg van der Waals radius, but within the limits of reliability of our molecular models this uncertainty would not affect our conclusions.) From the models the number of possible intermolecular contacts of each halogen atom were determined for each adduct; this number plus 1 for the shorter covalent Hg-X bond gives the predicted halogen coordination numbers CN(X1) and CN(X2) shown in Table I. (In some cases the steric fits were too tight to predict the presence or absence of a certain intermolecular contact, given the simple nature of our models; two numbers are then listed for CN(X) in Table I.) The predicted coordination number of the mercury atom (CN(Hg)) is then given by eq 1. Although these compounds CN(Hg) = YI + CN(X1) + CN(X2)
(1) generally show the expected26pseudooctahedral coordination about mercury, the small 59-64' bite of the OCHzCHzO chelate allows the possibility of seven-coordination and even hexagonal-bipyramidal eight-coordination, in some of the adducts (Table I), while the large size of the tert-butyl groups in HgXpdiglytbu might cause five-coordination. The prediction for HgClTtetragly is, of course, confirmed by the x-ray structure;24the listed coordination numbers for the mercuric halides t h e m s e l ~ e s ~and ~ - ~for ~ HgBrpTHF,30 HgC122CH30H,3 H g C l ~ d i o x(diox ~ ~ = dioxane), and H g B r 2 2 d i o ~ ~ ~ result from x-ray structures. Having predicted the factors which will influence the frequencies of these compounds, we expect, according either to the Townes-Dailey a p p r o ~ i m a t i o nor~ ~to considerations of the Sternheimer effect34that (a) increasing CN(Hg) should, by pushing or polarizing electrons toward the halogen, lower the halogen NQR frequency and (b) increasing CN(X1) or CN(X2) should, by removing electrons from the px (and perhaps py) orbitals of the halogen or by polarizing the np,
I 110
I
I
120
130
"Br Frequency, M H z
I
coo
I
Figure 1. Correlation of 35Clvs. 8'Br NQR frequencies of pairs of compounds QHgX,donor. Individual points are listed in the supplementary material.
+
+
and np, orbitals to increasing (n l)px and ( n l)p, character, also lower the NQR frequency of the halogen involved. Relationships among the Different Spectroscopic Measurements In order to understand how the 35Cl NQR data relate to the 81Brdata, we noted the observation of Brill7 that many chlorine and bromine NQR frequencies in analogous adducts of the same Lewis base show excellent correlations and thus are reasonably certain to have the same general structural features. In Figure 1 we have plotted all available2-'* pairs of 35Cland 81Br NQR frequencies taken at the same temperature for mercury chloride and bromide derivatives having the same empirical formula (except for chlorine and bromine), Most points do indeed fall near a common straight line, including compounds such as yC5C15HgX and CsClsHgX-gly, which are strongly suspected of being i s o s t r ~ c t u r a l .Falling ~~ far from the line are HgX2 and trans-ClCH=CHHgX, which are known not to be i s o ~ t r u c t u r a l . ~Points ~ , ~ ~ connected ,~~ by bars in Figure 1 show different multiplicities in their C1 and Br NQR frequencies and hence clearly are not exactly isostructural. The least-squares fit of all points in Figure 1 gives a line of slope 0.156, in reasonable agreement with the ratio of atomic quadrupole coupling constants34of 35C1and 0.171. We propose that, if the point for a mercuric chloridemercuric bromide derivative falls a distance of more than 2% of the chlorine or bromine frequency from the line of Figure 1 (the justification of 2% will be presented later), the bromide and chloride should be suspected not only of being crystallographically nonisostructural but also of having some molecular dissimilarities, such as differences in n, CN(X), or CN(Hg). Eliminating these points from the correlation gives a new line described by eq 2; the correlation coefficient im~ ( ~ ~ (= 2 0.165v("Br) 1) - 1.800
(2) proves from 0.922 to 0.964. A similar comparison of 81Brand 1271frequencies can be carried out, with somewhat less satisfactory results, since 81Br and 1271 have different spins. Therefore their NQR frequencies depend in a different way on their quadrupole coupling constants and asymmetry parameters. Using all available literature data we obtain the correlation v(b'Br) = 0.800~('*~1) - 0.002
(3)
The slope expected, ignoring the asymmetry parameter and the different polarizabilities of the halogens, is 0.935. De-
Mercuric Halide Adducts of Polyethers
Inorganic Chemistry, Vol. 15, No. 8, 1976 1793
Table 11. NQR Frequencies of Polyether Adducts and Related Compounds Compd 3'C1(77 K) 35cia
BP
7'BP
22.050 22.230 19.628e 21 .014e 20.454 20.052 20.205 21.137 (12) 20.957 (7) 21.846 (7) 21.400 (5) 22.116 (5)
128.4' 129.4' 130.22e 136.74e 133.70'
153.74 154.86
159.95 161.82
160.03
172.77
139.5 (69) 138.7 (50) 143.1 (50) 140.3 (4) 142.0 (5)
167.1 (81) 165.9 (27) 171.1 (22) 167.8 (2) 169.5 (4)
21.603 (11)
141.7i 13 9.3bj 142.9"j 142.08' 141.7 (63)
168.7h 165.5! 171.0' 170.07 169.9 (60)
174.3 (31)
132.9 (9) 133.1 (6)
158.9 (6) 159.2 (3)
163.0 (9) 174.9 (4)
136.5 (10)
163.1 (3)
176.4 (2)
HgX,
22.522 22.874 19.272" 20.584d
HgX,.THF HgX, ,dioxf HrCl, -~ .2CH OHe HgXzdYg HgX,.digly HgX .digly tb u
21.325 21.094 22.287 21.880 22.593
(74) (7) (9) (7)
(8)
a-HgX, .trigly p-HgX, .trigly
22.144 (19)
HgX, .2dioxf HgX,.tetragly
21.21 21.084 (5) 21.488 (5) 20.590 (5)
HgX ,. 18-crown-6 2HgX, .hexagly
21.15 20.869 21.213 20.231 20.215 20.468 20.966
(7) (7) (3) (1.5) (1.5) (3)
1211a
175.5 175.5 176.6 178.6
(19) (4) (4) (6)
170.4 (3) 175.0 (3)
Frequencies in MHz, at room temperature (297-304 K) unless otherwise indicated. Signal-to-noise ratios (SIN)in parentheses. Data from ref 2 and 6. Computed using Q(79Br)/Q(81Br)= 1.197. Data from ref 4. e Data from ref 7. Data from ref 9. g HgCI,.gly data, 77 K , agree with ref 4, while ref 8 gives 21.80 MHz, 77 K. "Br data have been reported for HgBr,.gly at 77 K: 140.40 and 141.23 MHz in ref 4 ; 141.19 and 143.75 MHz in ref 8. HgI,.gly (77 K) in ref 8 is assigned 180.06 MHz. At 312 K ; S / N = 3 for p-form 79Brlines and 8 for &-form 79Brline. At 308 K ; SIN = 25 for p-form "Br lines and 4 for a-form Br line. At 302 K ; SIN = 70 for p-form Br lines and 25 for p-form 7yBrline; a-form lines absent. a
viations of greater than 2%from this correlation may suggest molecular dissimilarities or (if the iodine frequency is too high) an asymmetry parameter of the order of 0.17 or higher. In comparing 35Cland 81BrNQR results on mercury halides and their adducts, it must be remembered that the structure of HgC1227is quite different from that of the isostructural pair HgBr228and yellow Consequently the point in Figure 1 corresponding to HgCl2 vs. HgBr2 shows the greatest deviation from eq 2 of any pair of compounds. From Figure l one may predict that if HgC12 had the HgBrz structure, it would have room-temperature frequencies of 19.3 and 19.4 MHz, rather than the observed 22.05 and 22.23 MHz. From its crystal structure HgBr2 clearly has CN(Hg) = 6 and CN(X1) = CN(X2) = 3. But the crystal structure of HgC12, which is frequently misinterpreted26 as indicating CN(Hg) = 6, is quite difficult to interpret. In a sense CN(Hg) = 8 and CN(X) = 4, since there are three31pairs of intermolecular Hg-Cl contacts. Two of these intermolecular distances, 3.54 and 3.40 A, slighti exceed the sum of conventional van der Waals radii, 3.30 while the third distance, 3.23 A, is only slightly under the sum.31 All may be under the sum of revised van der Waals radii. Hence CN(Hg) is uncertain in HgC12; for purposes of reference in our discussion we use the 19.3and 19.4-MHz frequencies of a hypothetical HgC12 which is isostructural with HgBrz and has CN(Hg) = 6 . In his work on the chloro anions of mercury, Scaife'O noted a good correlation between the Hg-C1 stretching frequencies and NQR frequencies for the compounds he was studying. We find that the same correlation can be applied even more successfully to these frequencies in the polyether adducts of HgCl2 and CsC15HgC1;16the combined correlation is shown in Figure 2. This suggests an opportunity to extend this study to dissolved adducts, which cannot be studied by NQR, and it suggests that the same factors which determine the NQR frequencies of the solids may determine the more readily accessible ir stretching frequencies. Results and Conclusions In Table I1 are presented the NQR spectra which we measured for the mercuric halide-polyether adducts, together
1,
Figure 2. Correlation of H g C l ir stretching frequencies vs. 300 K "Cl NQR frequencies for selected mercurials (HgCl,.donor, HgC1,("-2)-, C C1, HgCbdonor).
with previously known data for several other adducts of known crystal s t r ~ c t u r e s . ~ OThe - ~ ~frequencies for 35C1 are plotted in Figure 3 with square points as a function of the number of oxygen donor atoms, n. HgClyhexagly and HgClzdiglytbu are omitted, while the n = 1 point represents H g C L T H F (THF = tetrahydrofuran) and the n = 0 points represent the real and the hypothetical values for HgC12. (A similar curve can be drawn for the 81Bror 79BrNQR data, but for 1271 the results are different.) Table I11 presents the solid-state and benzene solution data for the ir Hg-Cl stretching frequency. The solid-state ir data correlate well with the 35Cl N Q R freqnencies of these
1794 Inorganic Chemistry, Vol. 15, No. 8, 1976
1
Gary Wulfsberg
@\ \
23
\ \
b
\
\ \ \
ti I
I
19' 0
t
2
3
4
5
6 Number of Oxygen Donor A t o m s
Number of Oxygen Donor Atoms
Figure 3. "Cl NQR frequencies of selected polyether adducts of HgC1, vs. the number of oxygen donor atoms n. Solid line connects solid-state NQR frequencies; broken line connects points derived from solution ir data using Figure 2.
Table 111. Hg-Cl Stretching Frequencies of Adducts' Adduct HEC1, HgCL.glY HgCl,.digly HgCl,.diglytbu HgCl,.trigly HgCl,.tetragly HgC1,.18-crown-6 2HgC1, ,hexagly
Solid
Solnb
313 355 363 368 368 35 8 341 353
393 380 314 368 369 367 344 361
In benzene solution; all spectra also a Frequencies in cm-' , showed lines at 393 cm-! attributed t o free HgC1,.
compounds, as indicated in Figure 2, but when the 35ClNQR frequencies of the two chlorines are split, as for n = 1 and n = 3, there is still only one v(Hg-C1) apparent. The solution ir data are quite different, however, and selected values (converted via Figure 2 from cm-' to MHz) are plotted in Figure 3 with circles. The solution spectra suggest a relatively smooth drop in u(Hg-C1) as n increases from 0 to 6 (with a minor deviation for n = 5, which will be discussed in the section on applications). This corresponds to the drop in WQR frequency expected from increasing factor 3, the number of donor atoms n about mercury. Evidently, then, factor 4, the number of intermolecular interactions, is constant (or smoothly changing) in this series of adducts in solution. Evidence of weak dimeric association of HgCh in benzene has been reported;38 however molecular weight determinations in benzene solution (Galbraith Laboratories) suggest a monomeric formulation for MgClrdiglytbu (calcd mol wt 490, found 494) and HgC12 trigly (calcd mol wt 450, found 448). Also, the solid-state data for HgClytetragly fit this curve, and HgClztetragly is known24 to be monomeric in the solid state. The solid-state NQR spectra, in contrast, show a peculiar "double-step function" until n = 4,after which they behave much as do the solution ir spectra. For n = 4, 5, and 6 (Le,, HgClytrigly, HgClytetragly, and HgC12-18-crown-6) a monomeric formulation is suggested, as was hypothesized in Table I. The diglyme, glyme, and T H F adducts behave differently; in Table I these adducts had been predicted to have (or possibly to have) CN(X1) or CN(X2) greater than 1, Le.,
Figure 4. Donor atom table: all reported 35ClNQR frequencies of HgC1, edducts of oxygen donors vs. most likely number of oxygen donor atoms n. Superscripts give CN(X) when known or deduced via molecular models; b , polyether adducts;Q, N-oxide or S-oxide adducts; m , other adducts.
to have intermolecular interactions. The diglyme (n = 3) and T H F (n = 1) adducts were predicted to have CN(X1) # CN(X2); it is these adducts which show large splittings in their 35ClNQR spectra. Furthermore comparison of Table I and Figure 3 shows that (for n less than 5, Le., mercury pseudooctahedrally coordinated) if a particular chlorine is predicted to have CN(X) = 3, its frequency is about 19.6 MHz; if CN(X) = 2, then its frequency is 21.0 MHz; and if CN(X) = 1, then its frequency is about 21.7 MHz. (For xlBr these figures are 128-130, 136-139, and 142-143 MHz, respectively.) For higher numbers of intermolecular interactions the frequency is lower, as previously predicted. Hence this work tends to support the suggestion of Bryukhova et a1.18 that the factor of intermolecular interactions, which was formerly often overlooked, is very important in determining the NQR frequencies of mercury halides and their derivatives. We thus suggest that each additional H g C 1 interaction lowers the 35ClNQR frequency by 0.7-1.5 MHz, while (from the slope of the dashed line in Figure 3) each additional polyether donor atom lowers the 35Clfrequency by only about 0.6 MHz. Hence we propose that from the NQR data for an adduct of unknown structure and the postulated value for n (from analytical data), possible structures of the adduct can be derived. In Figure 4 all r e p ~ r t e d ~ 35Cl - ~ NQR data at room temperature of HgC12 adducts of organic oxygen bases are plotted as a function of n. For compounds of known structure, CN(X) is indicated beside each point. Two lines of slope -0.6 MHz/unit of n are drawn in to separate the approximate regions of differing CN(X). CN(Hg) can then be computed using eq 1. The boundaries are diffuse, however, because these adducts do not all possess oxygen donor atoms of equal basicity. Hence, in a given n column, the relative position within a given CN(X) region should indicate relative basicity (although crystal field variations must be taken into account). In the n = 2 column most of the data correspond to known crystal structures and so can be discussed particularly well. In this column the known x-ray and NQR data are as follows: HgClz-cycl~hexanedione,~~ 21.5 1 M H z ; ~HgC12*gly,21.1 37 MHz (this work); H g C l * . d i o ~ ,20.454 ~~ M H z ; ~HgC12-2CH30H,3120.205 and 20.052 M H z ; ~HgClypy-N-0 (possessing
Inorganic Chemistry, Vol. 15, No. 8, 1976 1795
Mercuric Halide Adducts of Polyethers
Table IV. Possible Structural Interpretations of Literature NQR Data' for HgX, (X = C1, Br) Adducts
n 1
CN(Hg)
6
1 1 o r 2'
4 0 4 or 5'
3 4
6 7
0 0 0 1
2d 4
2 2
4 6
3 4
5
6 5
6
5
7
6
8
Compds fitting this pattern
CI sptittingb
BI splittingb
A . CN(X,) = 2, CN(X,) = 3 HgX, .acetophenone, HgX, .THF
1.476, 1.386
1.24, 6.52
0.943 1.401, 1.109
2.9lC 9.18 9.18 4.4 3.6, 3.4
B. CN(X,) = 1 , CN(X,) = 2 HgX, .benzophenone HgX, .y-pic-NO, HgCl, .DMSO, HgBr, .py-N-O HgX,.digly, HgCl, .diglytbuc HgBr,.trigly-p, 2HgX,,hexaglyc
0.889, 0.716 0.498,0.751
C. CN(X,) = CN(X,) HgCl, C,Cl,HgCl HgC4 HgBrz HgBr,.benzophenonec HgC1, .cyclehexanedione HgX,.gly, HgX,.diox, HgCl,.benzoquinone, HgC1,.2CH30H, HgCl,.py-N-O, HgCl,.DMSO (77 K), HgC1, .DMF, HgC1, .dimethylpyrone, HgBr .2 (phenoxathiin) HgX,.diglytbu,' 2HgX,.hexaglyc*e 2HgX,.hexagly:Ie HgX,.trigly-oc, HgX, .2diox, HgBr, Stetragly HgC1, .tetragly HgX2.18-crown-6
,
0.0 1-0.15 0.200 0.95 2.91
0 030 0, 0.153 0.439, 0.384 0.248, 0
030
1.27 1.7,O 030 030
0.716,O 0.253,O 0 0.34 0
0
'
Differences in frequencies (in MHz) between two lines of the NQR spectrum Literature data from ref 4-9 and 16 and from this work. for 35Clor 81Br. Alternate interpretations also possible. Not counting possible additional coordination b y organic n systems or organic chlorines. e NQR data for one of two inequivalent HgX, molecules in the unit cell.
bridging N-oxide groups, therefore two oxygen donor functions per mercury),40 19.461 and 19.022 M H z . ~ The cyclohexanedione adduct is highest in frequency because its CN(X) = 1; in all others CN(X) = 2. The order of frequencies then suggests that the basicities should fall in the order glyme < dioxane methanol < pyridine N-oxide. The greater basicity of pyridine N-oxide is reasonable in terms of the partial negative charge on oxygen. The apparent low basicity of glyme may result from the small 0-Hg-0 bond angles. This (approximately) 60' angle is not optimal for overlap with the mercury 6p orbitals. This result can also be seen in the n = 4 column. The flat lines in the left part of Figure 3 also suggest that the basicity toward mercury of glyme oxygen is about equal to the basicity of chloride covalently bonded to mercury, since replacement of one donor atom with the other does not alter the frequency. Given the data needed to use Figure 4 and a preconception of the relative basicity of the oxygen donor atoms, it is then possible to predict the structure, or a few alternate structures, for an adduct. Since mercuric halide adducts of oxygen-donor ligands usually have a pseudooctahedral structure,26one would generally expect CN(X1) # CN(X2) and hence large splittings for odd values of n. For even values of n one would generally expect CN(X1) = CN(X2) structures and small NQR splittings. The known NQR data are used to predict possible structures in Table IV. Of particular interest are compounds which are predicted to have CN(Hg) # 6. These are the compounds likely to have unusual features of special interest to crystallographers. Finally, it is useful to examine the magnitudes of the splittings of the NQR frequencies in these adducts. Among the adducts with CN(X1) # CN(X2), it appears that larger splittings are observed for adducts of N-oxide and S-oxide ligands, probably due to the larger point charges present. Omitting these ligands, we note that the splittings seem to be larger for CN(X1) = 2, CN(X2) = 3 (1.4-1.5 MHz for 35Cl and 6.5-7.2 MHz for 81Br) than for CN(X1) = 1, CN(X2) = 2 (0.5-0.9 N H z for 35Cl and 2.9-4.5 MHz for *lBr), although there are not many examples of each type. This does not necessarily mean that there is any meaningful difference
-
in the splittings of the quadrupole coupling constants, however, since the frequency also depends on the asymmetry parameter
+
e*& (1 $/3)"2 (4) 2 For CN(X) = 1 there should be substantially no asymmetry parameter. Since there is no threefold or higher symmetry axis for the halogen if CN(X) = 2 or 3, there would be an asymmetry parameter in these cases, which by (4) would raise the frequency slightly and reduce the splitting observed between CN(X) = l and CN(X) = 2. It follows from the use of Figure 4 that the largest splittings must be associated with the assignment of CN(X)1 # CN(Xz), but there appear to be few splittings of intermediate magnitude (0.45-0.8 MHz for 35Cland 2-4 MHz for *lBr). These few cases occur in adducts where the intermolecular interactions may be sterically hindered. Hence, except for these cases, it may be possible to distinguish large splittings due to intermolecular interactions from small splittings due to crystallographic inequivalence of halogens in adducts in which CN(X1) = CN(X2). These crystallographic splittings (omitting N-oxides and the uncertain intermediate cases) appear to range from 0 to 0.4 MHz for 35Cland from 0 to 2.9 MHz for 81Br,Le., about 2% of the NQR frequency. This small splitting, if confirmed by structural studies of the intermediate cases, would seem to suggest the absence of any great ionic contributions to the lattice electric field gradient and therefore to the bonding in the mercuric halides themselves or to the mercury-ligand bonding. Applications Of particular interest are cases where CN(X1) + CN(X2) + n do not seem to add up to a coordination number of 6 for mercury. Several such cases turned up in this study. One such case is the series of adducts HgXpdiglytbu (X = C1, Br, I). The molecular models suggest that the bulky tert-butyl groups hinder each other in the possible dimer with CN(Hg) = 6, unless the tert-butyl groups adopt an axial configuration, in which case they bump the lone pairs of the halogen (especially chlorine). Use of Figure 3 and its Br and I equivalents suggests or
~(35,37C1
79381~~ =)
1796 Inorganic Chemistry, Vol. 15, No. 8, 1976
that CN(Hg) = 5 for HgX2-diglytbu (X = Br, I). For X = Cl, however, the data are uncertain: there is a substantial (but smaller than expected) splitting of the 35Clfrequencies, which might suggest formation of a dimer. However, there is no appreciable difference in temperature d e ~ e n d e n c eand , ~ ~the identical natures of the solid-state and solution ir spectra suggest the same degree of aggregation in both (which is monomeric, in solution). The triglyme adducts also show some very interesting results. According to the models, the coordinated trigly ligand occupies virtually the same volume as the diglytbu ligand but of course has one more donor atom. Hence the same two possibilities, but with CN(Hg) being 1 higher and NQR frequencies presumably being lower, exist. HgClTtrigly has only one NQR frequency, so both chlorines must have CN(X) = 1. HgIytrigly, however, has two substantially split frequencies in the proper range to suggest CN(X1) = 1, CN(X2) = 2 , CN(Hg) = 7. Most interesting is the compound HgBrzmtrigly, which shows a phase transition just above room temperature. At 302 K the NQR spectrum indicates the compound to be isostructural with the iodide adduct, with two frequencies and a dimeric structure. At 308 K these two lines begin to fade and a new line grows in between the two. At 312 K only the new frequency remains, at a value which indicates the same structure as the chloride monomer. The tetraglyme adducts show an irregularity; I ~ a m o t o * ~ reported that the bromide adduct was not isostructural with the chloride adduct, and our NQR frequencies confirm this: both the bromide and iodide give only one signal which is too high to correspond to that of the chloride. In fact the spectra do correspond with the monomeric form of HgXytrigly (X = C1, Br), which suggests the possibility that the effective number of donor atoms in the bromide and iodide adducts is only 4. The infrared spectra of the tetraglyme ligand in the bromide and iodide are virtually superimposable,but there are some small differences between these ir spectra and that of the chloride. Hence there may be a different conformation of the ligand in which one oxygen is not coordinated to mercury, or the two end oxygens are each weakly coordinated. The high Hg-C1 stretching frequency of HgCl2-tetragly in solution suggests that the same thing may happen to the chloride adduct in solution. Some data, of course, have more than one quite satisfactory explanation. Such is the case for 2HgX~hexagly,which has not yet been discussed. For these compounds n is computed to be 3.5, which could mean n = 3 for one mercury and n = 4 for the other. This gives one satisfactory interpretation, featuring one five-coordinate mercury. On the other hand, Iwamoto has done the x-ray structure24 of the very closely related complex ~ H ~ C ~ T C ~ H ~ ( ~ C H ~and CH found ~)~O the central oxygen to be bridging, both CN(Hg) values being 7. Assuming this for the HgCL and HgBn adducts also gives a satisfactory fit to Figure 4. Other distributions of the available donor atoms also gave satisfactory fits but on examination with molecular models proved sterically impossible. Acknowledgment. The author wishes to thank Robert West for the use of his laboratories and NQR spectrometers, Reikichi Iwamoto for providing the report of the x-ray structures of the polyether adducts,23and Marlys Wulfsberg for help in preparing the manuscript. Registry No. HgClygly, 591 87-92-7; HgBrzagly, 59187-94-9; HgClydigly, 59187-71-2; HgBrydigly, 59187-72-3; HgIz-digly, 59 187-73-4; HgClzdiglytbu, 59 187-74-5; HgBrydiglytbu, 59 187-75-6; HgIz-diglytbu, 591 87-76-7; HgCITtrigly, 40237-14-7; HgBr2-trigly, 59187-77-8; HgITtrigly, 59187-78-9; HgClptetragly, 40802-28-6;
Gary Wulfsberg HgBrTtetragly, 59187-79-0; HgIzqtetragly, 59187-64-3; HgC12.18crown-6, 59187-80-3; WgBrz.18-crown-6, 59187-81-4; HgI2.18crown-6, 591 87-82-5; 2HgClyhexagly, 591 87-83-6; ZHgBrphexagly, 59187-84-7; 2 H g I ~ h e x a g l y , 59187-85-8; 35CI, 13981-72-1; *IBr, 14380-59-7; 79Br, 14336-94-8; Iz7I2, 7553-56-2.
Supplementary Material Available: A listing of analytical data and melting points of these adducts and complete data for correlations of 3sCl, slBr, and lZ7INQR frequencies ( 3 pages). Ordering information is given on any current masthead page.
References and Notes (1) (a) A preliminary report of this work was given at the 169th National Meeting of the American Chemical Society, Philadelphia, Pa., April 1975; see Abstracts, No. INOR 114. (b) Address of the author for 1976: Physikalische Chemie 111, Technische Hochschule, 6100 Darmstadt, West Germany. (2) Data and references cited in I. P. Biryukov, M. G. Voronkov, and I. A. Safin, “Tables of Nuclear Quadrupole Resonance Frequencies”, Israel Program for Scientific Translations, Jerusalem, 1969. (3) D. Biedenkapp and A. Weiss, Z . Naturforsch., A , 19, 1518 (1964). (4) E. V. Bryukhova, “Doklad na Simpoziume po YaMR i YaKR, Tallin, 1967”, cited in Yu. K. Maksyutin, E. N. Gur’yanova, and G. K. Semin, Russ. Chem. Reo. (Engl. Transl.), 39, 334 (1970). (5) T. B. Brill and Z Z. Hugus, Jr., Inorg. Chem., 9, 984 (1970). (6) T. B. Brill, J . Inorg. Yucl. Chem., 32, 1869 (1970). (7) T. B. Brill and Z Z. Hugus, Jr., J . Inorg. Nucl. Chem., 33, 371 (1971). (8) E. V. Bryukhova, N. S. Erdyneev. and A. K. Prokof‘ev, Bull. Acad. Sci. USSR, Diu. Chem. Sci., 1846 (1973). (9) D. B. Patterson, G. E. Peterson, and A. Carnevale, Inorg. Chem., 12, 1282 (1973). (10) D. E. Scaife, Aust. J . Chem., 24, 1753 (1971). (11) V. I. Bregadze, T. A. Babushkina, 0.Yu. Okhlobystin, and G. K. Semin, Theor. E x p . Chem. (Engl. Transl.), 3. 325 (1967). (12) T. A. Babushkina, E. V. Bryukhova, F. K. Velichko, V. I. Pakhomov, and G . K. Semin, J . Struct. Chem. (Engl. Transl.), 9, 153 (1968). (13) E. V. Bryukhova,T. A. Babushkina, M. V. Kashutina, 0.Yu. Okhlobystin, and G. K. Semin, Dokl. Chem. (Engl. Transl.), 183, 1035 (1968). (14) A. N. Nesmeyanov, 0.Yu. Okhlobystin, E. V. Bryukhova, V. I. Bregadze, D. N. Kravtsov, B. A. Faingor, L. S. Golovchenko, 2nd G. K. Semin, Bull. Acad. Sci. USSR, Dic. Chem. Sei., 1785 (1969). (15) T. B. Brill and 6. G. Long, Inorg. Chem., 10, 74 (1971). (16) G. Wulfsberg, Ph.D. Thesis, University of Wisconsin, 1971. (17) E. V. Bryukhova and G. K. Semin, Chem. Commun., 1216 (1971). (18) E. V. Bryukhova, A. K. Prokofev, T. Ya. Mel’nikova, 0.Yu. Okhlobystin, and G. K. Semin, Bull. Acad. Sci. USSR, Diu. Chem. Sci., 448 (1974). (19) Yu. S. Grushko, A. Yu. Aleksandrov, 0. Yu. Okhlobystin, V. 1. Gol’danskii, and A. N. Murin, J . Struct. Chem. (Engl. Trawl.), 13,977 (1972); H. Sakai, Y. Maeda, S. Ichiba, and H. Negita, Chem. Phys. Lett., 27, 27 (1974). (20) W. Gordy and J . Sheridan, J . Chem. Phys.. 22, 92 (1954). (21) C. Feige and H. Hartmann, Z . Naturforsch.. A , 22, 1286 (1967). (22) T. B. Brill, J . Chem. Phys., 61, 424 (1974). (23) I . M. Kolthoff and P. J. Elving, Treatise Anal, Chem., 3, 289 (1961). (24) R. Iwamoto, “Report of the Government Industrial Research Institute. Osaka, No. 342”, Midorigaoka 1, Ikeda City, Osaka, Japan, 1972; R. Iwamoto, Spectrochim. Acta, Part A , 27, 2385 (1971); R. Iwamoto, Bull. C h e m S o c . Jpn.,46, 1114, 1118, 1123, 1127 (1973). (25) P. Groth, Acta Chem. Scand., 25, 3189 (1971); J. D. Dunitz, M. Dobler, P. Seiler, and R. P. Phizackerley, Acta Crystallogr., Sect. B, 30, 2733 (1974): P. Seiler, 41.Doblcr, and J . D. Dunitz, ibid., 30, 2744 (1974). (26) D. Grdenic, Q. Rec.., Chem. Soc., 19, 303 (1965) (27) H. Braekken and W. Scholten, Z . Kristullogr., Kristallgeom., Xristullphys., Kristallchem., 89, 448 (1934); D. Grdenic, A r k . Kemi, 22, C~H ~ 14 (1960). (28) H. BraeLen, 2. Kristallogr., Kristallgeom., Kristallphys., Kristallchem., 81, 152 (1932); H. Verweel and J. M. Bijvoet, ibid., 77, 122 (1931). (29) G. A. Jeffrey and M. Viasse, Inorg. Chrm., 6, 393 (1967). (30) M. Frey, H. Leligny, and M.Ledesert, Bull. Sac. Fr. Mineral. Cristallogr., 94, 467 (1971). (31) 13. Brusset and F. Madaule-Aubry, Bull. Soc. Chim. Fr., 3121 (1966). (32) 0. Hassel and J. Hvoslef, Acta Chem. Scand., 8, 1953 (1954). (33) M. Frey, C. R. Hebd. SeanceA Acad. Sci., Srr. C, 270,413 (1970); M. Frey and J.-C. Monier, Acta Crystallogr., Sect. 5, 27, 2487 (1971). (34) E. A. C. Lucken, “Nuclear Quadrupole Coupling Constants”, Academic Press, New York, N.Y., 1969. Chapters 5 and 7. (35) G. Wulfsberg, R. West, and V. N. M. Rao, J . Organomer. Chem., 86, 303 (1975). (36) A. I. Kitaigorodskii, izc..A k a d . Nauk S S S R , Ser. Khim., 260 (1947). (37) V. I. Pakhomov and A. I. Kitaigorodskii, J . Struct. Chem. (Engl. Trans/.). 7, 798 (1966). (38) I. Eliezer and G. .4lgavish, Inorg. Chim. Acta, 9, 257 (1974). (39) P. Groth and 0. Hassel, Acta Chem. Scand., 18, 1327 (1964). (40) G. Sawitzki and H. G. van Schnering, Chem. Ber., 107, 3266 (1974).
